The present invention relates generally to infusion pumps for administering intravenous fluids and more particularly to a specific type of peristaltic infusion pump which utilizes a specifically designed disposable cassette.
Infusion pumps are being used increasingly to administer intravenous (IV) fluids in intensive and coronary care units, laboratory and delivery rooms, and neonatal and pediatric departments as a replacement for the traditional gravity flow system. There are a number of different types of infusion pumps ranging from the relatively simple syringe type to the more complicated piston and cylinder and peristaltic types. Inasmuch as the present invention relates only to peristaltic infusion pumps, the present discussion will be so limited.
There are presently a number of specifically different peristaltic type infusion pumps either on the market or in the prior art generally. Obviously, these particular types of pumps have in common the fact that each utilizes peristaltic action on a tube for moving the fluid through it. In a typical linear pump, a series of finger like projections sequentially advance and retract to move the fluid toward the patient. In a typical rotary type pump, a plurality of rollers which are attached to a rotating disc alternately squeeze and release a section of tubing to move the fluid towards the patient. As will be seen hereinafter, the present invention relates more to the rotary type of pump than the linear type.
One example of a previously suggested rotary type peristaltic infusion pump is disclosed in U.S. Pat. Nos. 3,927,955 (Spinosa), dated Dec. 23, 1975 and 3,841,799 (Spinosa), dated Oct. 15, 1974. Each of these patents discloses what is referred to as a medical cassette pump which includes a single, continuous fluid-carrying tube for delivery of fluid from a fluid dispensing bottle to the patient. A section of this tube is positioned within the cassette and against the base or bases of the cassette so as to define an arcuate path which is substantially greater than 180.degree. and, in at least one embodiment, almost a full 360.degree.. A plurality of rollers located within this arcuate path act upon the supported tubular section for peristaltically moving liquids therethrough.
The peristaltic pump described in the Spinosa patents does have one advantage over some peristaltic pumps in the prior art. Specifically, Spinosa states that his cassette may be assembled with the tube, and furnished as a unit, each unit constituting a complete disposable cassette. However, there are certain disadvantages with the particular pump disclosed in these patents. In the first place, Spinosa utilizes a single continuous tube. If the particular section of this tube subjected to the peristaltic action is to withstand the typical abuse it will be subjected to, it must be of relatively high quality. However, this could be relatively expensive compared to the overall costs of the cassette. On the other hand, it certainly does not seem wise to utilize a tube which cannot withstand the intended and expected abuse it should receive during its useful life in order to minimize cost. In the second place, it should be noted that this tube is not fixedly held in place as it enters what Spinosa calls his cassette and it is not fixedly held in place as it leaves the cassette. As a result, there is a tendency for the tube to creep in the direction of the moving pump head. This, in turn, can adversely affect the accuracy of the pump and can cause the tube to stretch out of shape. Moreover, it can actually cause the tube to separate from its fluid dispensing bottle.
Another type of peristaltic pump suggested by the prior art, actually made available in the prior art, is one which includes a short length of its flexible tubing anchored at its opposite ends to stationary holding blocks. The mid portion of this tubing which is referred to as a pump chamber is stretched taut around three cylindrical rollers arrayed in a triangle on a rotor plate. The pump chamber is of course connected at one end to a reservoir of fluid (an IV bottle) and at the other end to the patient. In operation, the pump chamber, that is the flexible tubing, is pinched shut where it bends sharply around the rollers, but the lumen remains open between rollers. When the rotor plate turns, the points of occlusion advance along the pump chamber tube, and the fluid between them is pushed to the outlet end of the tube, as fresh fluid is drawn from the reservoir into the inlet end. The flow rate through this pump chamber, i.e., through the tube, depends upon the diameter and elastic properties of the tube and on the speed of the motor turning the rotor plate. While the speed may be set with a control knob so that the flow rate can be varied, this is only provided to a limited degree and, in actuality, three or more different tubes are required to cover a flow rate range of between 0.33 and 650 cc/hr.
While the peristaltic pump just described will most likely not creep because its ends are tied down, it does have certain other disadvantages. For example, this particular pump does not utilize or suggest utilizing a separate cassette at all but rather connects the tubing directly to the pump apparatus. This can be quite cumbersome and, more important, it can possibly lead to improper assembly of the tube around the pump head. Moreover, because of the particular way the tubing is arranged around the pump head, it is susceptible to stretching which in turn results in a change in flow rate resulting in inaccuracies. Further, this particular type of pump relies on a number of tubes to give a relatively wide low rate range which, of course, is time consuming and complicated.
As will be seen hereinafter, the present invention is directed to a particular peristaltic infusion pump and a particular disposable cassette, including tubing, for use with the pump. As will also be seen, this overall pump assembly, which is constructed in accordance with the present invention, does not have the various disadvantages discussed above.